The present invention relates to a vibration-type angular rate sensor which drives and vibrates an oscillator to detect an angular velocity.
The vibration-type angular rate sensor is, for example, formed by etching a semiconductor substrate to form a base portion, an oscillator, and drive electrodes of this oscillator. According to this kind of angular rate sensor, alternating-current signals (i.e. drive signals) having mutually opposite phases are applied to a pair of drive electrodes to cause the oscillator to vibrate in the predetermined direction. If any angular velocity is applied in a condition that the oscillator vibrates regularly in the predetermined direction, the oscillator will start vibrating in a perpendicular direction due to a Coriolis force caused in response to the applied angular velocity. The vibration-type angular rate sensor has detection electrodes detecting a change in the electrostatic capacity occurring due to this vibration and detects the applied angular velocity.
According to this kind of angular rate sensor, thermal stresses applied from the outside to the sensor chip and/or vibrations transmitted from the outside to the sensor chip give adverse effects on angular velocity detect accuracy of the sensor. Therefore, the angular rate sensor is required to have sufficient capability of relaxing thermal stresses and assuring vibration-proof properties.
In this respect, the Japanese patent application Laid-open No. 2000-249562 (hereinafter, referred to as prior art 1) discloses an angular rate sensor capable of reducing a bonding area with appropriate hollow spaces provided on a package for relaxing the thermal stress. Furthermore, the Japanese patent application Laid-open No. 2003-21647 (hereinafter, referred to as prior art 2) discloses an arrangement capable of relaxing the thermal stress by using a silicone adhesive film to bond a sensor chip and a circuit chip. Moreover, the Japanese patent application Laid-open No. 2000-55667 (hereinafter, referred to as prior art 3) discloses an angular rate sensor capable of assuring vibration-proof properties with a rubber vibration isolator supporting a package mounting an oscillator.
However, the sensor arrangement of the above-described prior art 1 is disadvantageous in that additional processing (or machining) is required to form a complicated surface of the package. This will increase the manufacturing costs. Furthermore, the bonding strength between the oscillator and the package tends to be incomplete. This will deteriorate frequency characteristics of the entire sensor structure. Furthermore, the above-described prior art 2 discloses nothing about vibration-proof properties of the angular rate sensor.
Moreover, the angular rate sensor disclosed in the above-described prior art 3 requires additional parts to be specially prepared to improve the vibration-proof properties. This will increase the costs.